Cone Beam Computed Tomography (CBCT)-Based Online Adaptive Radiotherapy for Patients With Metal Implants: An Institutional Experience

Background Patients with metal implants (MIs) are often excluded from the current cone beam computed tomography (CBCT)-based online adaptive radiotherapy (oART) workflows because of concerns regarding imaging artifacts, potentially limiting access to this innovative technology. Purpose This study aimed to present our institutional experience treating patients with MI using an oART workflow and to evaluate dose accuracy and on-couch treatment time. Methods Eight patients treated at the Wilmot Cancer Center (University of Rochester, Rochester, USA) on the Ethos system were retrospectively analyzed, including five with MI and three without MI. During treatment planning, dosimetric avoidance through the MI was implemented to minimize dose deposition within the implants. The necessity of overriding metal artifacts (MAs) surrounding the implants was evaluated using 3D gamma analysis, as well as comparisons of Dmax, Dmin, and Dmean. The impact of MA on AI-based auto-contouring was assessed by comparing automatically generated contours with expert-modified contours using the Dice similarity coefficient (DSC) and maximum Hausdorff distance (MHD). Contouring times were also compared between patients with and without implants. Results Dosimetric avoidance through the MI achieved clinically acceptable plan quality. No clinically meaningful differences in dose distribution were observed between plans with and without MA overrides, suggesting overrides may be unnecessary unless MA overlaps with target volumes. Although the presence of MI and CBCT artifacts affected auto-contouring performance, they did not compromise the feasibility of oART delivery on the Ethos system. Contouring times were comparable between implant and non-implant patients. Overall, DSC and MHD values demonstrated good agreement between auto-contoured and manually edited structures, with the exception of the bladder. Conclusions Our proposed workflow demonstrates the feasibility of CBCT-based oART for patients with MIs based on institutional experience. Additional validation may be required to meet institutional standards and policy requirements.